1. Field of the Invention
The present invention provides a pump for delivering two different materials serially at a location at substantially the same flow rate and pressure. The pump is useful for consistently filling capsules with two different materials such that the internal pressure of the capsules is substantially uniform.
A resin capsule is commonly used for securing a bolt into a rock face to support the rock face, e.g, in a rock tunnel in a mine. A resin capsule generally comprises a tubular sheath of a frangible film, with a longitudinal barrier dividing the capsule into two compartments. The capsule is terminated by clips. Within the capsule, one compartment is filled with a mastic of polyester resin and fillers (usually limestone) and the other compartment is filled with a paste containing activator for the polyester resin, extended with fillers such as further limestone and water. The capsule typically has a diameter of 12-40 mm and a length of 300-3000 mm.
Resin capsules are manufactured continuously on “form-fill-seal” machinery. There are many variants of this machinery. Generally, the sheath is first formed by folding a web of film into a tube and continuously forming longitudinal seals and the internal barrier as the tube travels through the machine. At a short distance after the formation of the tube, nozzles inject the resin mastic and activator paste into their respective compartments. At later stages the terminating clips are affixed and the tube is severed between clips to form the discrete capsules. Typical output of such a machine is 12-25 meters of resin capsules per minute.
Customer requirements are that the capsules should have consistent mass, consistent internal pressure and consistent proportion between resin and activator components. These requirements are met by ensuring constant flow rates and pressures from the nozzles injecting the resin and activator components.
In resin-grouted rock bolting practice, there is commonly a requirement that two setting times of resin be used: a fast-set resin at the distal end of the rock bolt hole, and a slow-set resin nearer the collar. Use of the fast-slow combination makes installation of the bolt easier in holes more than about 1.5 m deep.
Various methods are used to place the two setting times of resin in the hole. The simplest is for the operator to separately load discrete capsules, the first-loaded capsule or capsules containing fast-set resin and the later loaded capsule or capsules containing slow-set resin, This method is slow and prone to operator error however.
A better method is to have the fast and slow resins in the same capsule, which will have one end filled with fast resin mastic and the other with slow resin mastic. Such a capsule is known as a two-speed capsule and is used on a large scale in Australia where capsules are sold under the trade names “TooSpeedie” and “Duospeed”. A two-speed capsule is believed to be manufactured by using parallel resin mastic pumping lines for the fast and slow components with the capsule forming machine switching between the two lines. It will be appreciated that delicate balancing of the two lines is necessary to achieve the switch without fluctuation of pressure or flow, and that this balancing must be regularly adjusted as the pumps wear.
2. Description of the Prior Art
Conventionally a pumping system comprising a pair of diaphragm pumps is used to fill normal capsules because it produces a constant flow and pressure. Such a system is described in U.S. Pat. No. 4,543,044. They are generally known as constant-flow diaphragm pumps and will be referred to herein as a CFD pump. The disadvantage of the CFD pump is its high initial cost. Each one is custom-made. The CFD pumping technology cannot be readily applied to the manufacture of two-speed capsules, due to the high capital cost of providing dual parallel CFD pumps.
An advantage of using a CFD pump is that, unlike a conventional progressing cavity pump (such as made by Mono or Moyno), it can be used to pump a mastic containing coarse particles of a filler. Thus a two-speed capsule is more expensive to manufacture by using a conventional progressing cavity pump because it contains more polyester resin and activator. Furthermore, whilst a progressing cavity pump is more readily available and cheaper than a CFD pump, it suffers from the limitations that the rotors and stators wear and need regular replacement; and that as the components wear there is a drift in flow rate and pressure, which makes long-term automatic control difficult.
As an alternative, a different method of achieving the two setting times of resin in the same capsule has been found. This method uses direct injection of an accelerator into a portion of the length of the capsule, in synchronisation with capsule formation. When the capsule is broken and the contents mixed during rock bolt installation, the accelerator mixes with the resin and transforms part of the resin from slow to fast. This method can be used in conjunction with the conventional method of manufacturing normal capsules, i.e. by using a CFD pump and including coarse filler in the capsule. Although the production line is relatively low-cost to build, this method has the disadvantages of reduced shelf-life of the capsules as the accelerator migrates inside the capsule; mixing of the accelerator with the resin in the rock bolt hole is not efficient such that the dosage of accelerator is much higher than in pre-blending fast resin mastic prior to injection; and the accelerator normally used (which is di-methyl paratoluidine) is a high-cost material.
Accordingly improvements in the production of two-speed resin capsules have been sought.